(53c) Secondary Organic Aerosols (SOA) from Nitrate Radical Oxidation of Monoterpenes: Results from Recent Laboratory and Field Studies

Secondary organic aerosols (SOA), formed from the oxidation of gas-phase hydrocarbons followed by gas-particle partitioning, make up a dominate fraction of OA. The reaction of biogenic volatile organic compounds with nitrate radicals (NO3) represents a direct mechanism in linking anthropogenic and biogenic emissions, but to what extent this affects aerosol formation and organic nitrates in the atmosphere is poorly understood. We performed both laboratory chamber studies and field measurements to investigate SOA formation from nitrate radical oxidation of monoterpenes. A series of experiments was performed with b-pinene in the Georgia Tech Environmental Chamber facility (GTEC), in dry and humid conditions, under either “RO2+NO3” or “RO2+HO2” dominant conditions. For field measurements, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed in the southeastern US as part of Southeastern Center of Air Pollution and Epidemiology study (SCAPE) and Southeastern Oxidant and Aerosol Study (SOAS). Measurements were performed in both rural and urban sites in the greater Atlanta area and Centreville, AL for approximately one year. Chamber results showed that for a wide range of organic mass loadings (5.1-216.1 μg/m3), the aerosol mass yield is substantial, ranging from 27.0-104.1%. It is estimated that about 90 and 10% of the organic nitrates formed from the b-pinene+NO3 reaction are primary organic nitrates and tertiary organic nitrates, respectively. While the primary organic nitrates do not appear to hydrolyze, the tertiary organic nitrates undergo hydrolysis with a lifetime of 3-4.5 hours. Ambient measurements results showed that 50% of nighttime OA could be produced by b-pinene+NO3 during SOAS. The contribution of organic nitrates to total OA is estimated to range 5-12% in summer, suggesting that organic nitrates are important components in the ambient aerosol in the southeastern US.